The present application relates to inverters comprising a snubber and in particular to series resonant inverters comprising one or more capacitive snubbers. It finds particular application with radiology imaging modalities utilized in medical, security, and/or other applications. However, it also relates to other applications comprising inverters configured to produce an average power output that differs substantially (e.g., by a factor of 5 or more) from a peak power output and/or configured to output power over a large dynamic range.
CT and other radiography imaging modalities (e.g., single-photon emission computed tomography (SPECT), mammography, digital radiography, etc.) are useful to provide information, or images, of interior aspects of an object under examination. Generally, the object is exposed to radiation photons (e.g., such as X-rays, gamma rays, etc.), and an image(s) is formed based upon the radiation absorbed and/or attenuated by the interior aspects of the object, or rather an amount of photons that is able to pass through the object. Generally, highly dense sub-objects absorb and/or attenuate more radiation than less dense sub-objects, and thus a sub-object having a higher density, such as a bone or metal, for example, will appear on an image differently than less dense sub-objects, such as muscle or clothing.
The energy of radiation applied to an object is a function of the voltage applied to a radiation source emitting the radiation. Typically, the greater the voltage, the higher the energy. It may be appreciated that in some applications, such as in medical applications, it is desirable to alter the energy of radiation applied to the object as a function of the area being examined. For example, the energy of radiation applied during an examination of the brain may be less than the energy applied to image a foot because the brain comprises more delicate tissue than the foot. Moreover, although continued reference is made herein to imaging, it will be appreciated that radiation may also be utilized in the treatment of an object. In such applications, the energy of radiation may vary according to what is being treated and/or the pathway of radiation (e.g., whether the radiation passes through bone or merely soft tissue). Further, radiation in treatment and/or imaging modalities may be emitted in pulses, where respective pulses of radiation are followed by a resting period. While power supplied to the radiation source is reduced (e.g., to zero) during such resting times, a power supply may be configured to continue supplying power to other electronic components of the imaging modality.
It may be appreciated that in light of such conditions, a power source for a radiation imaging and/or treatment modality (e.g., particularly in medical applications where the energy of emitted radiation is varied widely), is configured to output power over a large dynamic range (e.g., 600 W or less when the source is not operating to 60 kW or more when the source is operating at maximum power, for example). Traditionally, the power source of a radiology modality has comprised an inverter, such as a resonant inverter, configured to convert direct current (DC) electrical signals into alternative current (AC) electrical signals at a desired voltage and/or to increase and decrease power dynamically (e.g., in a matter of nano- or microseconds) over a large range of various power output levels. To reduce switching losses in the inverter that occur when a switch is opened (e.g., turned off) and the voltage is increased, a snubber (e.g., such as a capacitive snubber) may be added to the inverter. The snubber is configured to reduce a rise time of the voltage, which in turn reduces the power dissipated during the transition (e.g., meaning switching losses are reduced).